For supplying current and voltage to a load with a high current uptake, such as a CPU (Central Processing Unit) in a computer, it is known how to employ switching converters having several converter stages connected in parallel. Each of these converter stages receives an input voltage and each of these converter stages provides a portion of the overall current required to supply the load. Each individual converter stage has an inductive storage element, where the input voltage is applied in accordance with a pulse width modulated signal that is generated for each converter stage. Control of the current uptake of an individual converter stage occurs in terms of the duty cycle of the pulse width modulated signal generated for the particular converter stage.
Suitable as the converter stages are both those working by the current control principle (Current Mode, CM) and those working by the voltage control principle (Voltage Mode, VM). CM converter stages and VM converter stages differ with respect to the generation of the pulse width modulated signal that controls the current uptake of the converter stages. Common to both of the two principles is that a control signal dependent on the output voltage is generated to produce the pulse width modulated signal.
In a CM converter stage, this control signal is compared to a ramp signal, which is proportional to a current flow through the inductive storage element of the converter stage. The steepness of the edges of this ramp signal will depend on the input voltage and the inductance of the inductive storage element of the converter stage. In a VM converter stage, a separate ramp signal generator is present to create the ramp signal.
One problem with the parallel connection of several converter stages that supply a load in common is that identical current uptakes for the converter stages—unless further steps are taken—can be achieved only if the individual converter stages are identical in construction and if the components used to realize the converter stages are identical in dimension. Differing parameters of the components result in unequal current loading of the individual converter stages. In extreme cases, this can lead to individual converter stages becoming overheated and thereby damaged.
In order to achieve uniform current distribution it is known to make one of the converter stages a master converter stage and to detect the output current of this converter stage. The other converter stages are slave converter stages whose output currents are compared to the output current of the master stage. A control signal, supplied to the individual converter stages across an external feedback control loop and dependent on the output voltage, is corrected in the slave converter stages depending on the comparison of the output current of the particular converter stage to the output current of the master converter stage so as to achieve identical current up-takes for the individual converter stages.